Fatigue behavior of Ti-6Al-4V ELI including mean stress effects

This paper investigates cyclic deformation, fatigue behavior, and failure mechanisms for Ti-6Al-4V ELI (extra low interstitial) with and without mean strain/stress. This type of titanium alloy is broadly used in the biomedical and aerospace fields, specifically for implants and structural components, respectively. Fatigue properties were obtained using the strain-life approach with the use of smooth uniform gage section specimens under axial fully-reversed loading. The influence of mean stress on fatigue behavior was studied using four different strain ratios, Rε. The generated fatigue data was used to assess some strain-based mean stress fatigue life prediction models, including Morrow, Smith-Watson-Topper, Walker, Kwofie, Ince-Glinka and a modified version of the Smith-Watson-Topper. These models offered acceptable results, specifically the Morrow approach which provided more accurate fatigue life predictions. Fractography analysis was conducted to determine the influence of material defects on fatigue life and no major differences were found for the different strain ratios considered. Overall observations indicate that inclusions found near the surface were of great influence on the fatigue behavior.